Determining which bonds are more polar

[Bita Ghanei 1F]

If you are comparing Mg-O and B-O, would Mg-O be more polar because Mg has a smaller radius than B?

Thanks in advance!

[Sebastian Lee 1L]

Mg-O is more polar than B-O because the electronegativity difference between Mg and O is higher than between B and O. I think you're mistaken in saying that Mg is a smaller radius than B, because I'm pretty sure that atomic radius increases as you go down and to the left of the periodic table. Mg has a larger radius so the nucleus will have less of a pull for electrons (lower electron affinity). Meanwhile, Oxygen has a small radius and high electron affinity so it will want to take more electrons. This difference in electronegativity accounts for the ionic character of bonds since one atom will "hog" the electrons more strongly than the other. Boron has a higher ionization energy than Magnesium, so it will be less likely to "give up" its electrons to Oxygen = Less polar.

[LReedy_3C]

The difference in electronegativity is the main thing that makes Mg-O more polar. This difference causes the electrons to be more strongly pulled to one nucleus rather than the other, giving the bond ionic character and making it polar.

[Sanjana Munagala_1j]

Wait this does not make sense. Do you by chance mean BaO instead of BO, because in that case MgO would be more polar since it has more covalent character due to a lower electronegativity difference. Furthermore, Mg2+ has more polarizing power than Ba2+ because it is a smaller cation and thus the effective nuclear charge is larger.

Hope that helps!

[Abigail Sanders 1E]

I believe that when comparing two different covalently bonded molecules the bond that is more polar is the bond with the largest difference in electronegativity.